Hello Disco community, I’m trying to solve some alternator whine in a new stereo head unit I installed in my ‘98 Discovery. I’d like to check the head unit ground and amp ground, but don’t know where they tie into the chassis. I’ve searched the workshop manual but can’t find that info. Does anyone know where I can find these to check for corrosion and bad grounds?

 

There are two main grounds. One on the left and the other on the right behind the side foot panels.

Each is identified by number (e.g. E200 and E201) in the Electrical Troubleshooting Manual (ETM). I saved a copy for my trucks. Sometimes called a RAVE manual. There are diagrams and descriptions of the ground circuits, including a ground connector behind the instrument binnacle. Each model year has its own wiring, even though similar to other years, so make sure you get the correct one. I think I need a signal isolator to solve the whine in my system, but have not bought one yet.

 

Thanks @JohnZo. I found the diagrams. The photos in the back of the manual are very helpful. I’ll get in there to see if a weak ground is contributing.

 

The ground wire should be securely connected to a clean, unpainted metal surface on the car's chassis, as this provides a stable electrical connection and minimizes issues such as static, humming, or audio dropouts.

 

I was able to check the grounds in the passenger and driver footwells and they look factory-new, so I’ll keep going down my troubleshooting checklist to find the source of the alternator whine. I looked through the forums and this seems to be a common issue for early Discos.

 

Problem solved. For those with similar issues, I cleaned the main battery ground which is just behind the battery and it cleaned up a lot of alternator whine. Look up E100 in the back of GEMS electrical manual for a picture of the ground location.

 

Documenting for others with similar symptoms. A month later I finally found and corrected the last bit of alternator whine. Two of the aftermarket spark plug wires had come out of their clips and were resting against the engine block, hidden from view. No metal to metal contact, just the rubber sheathing lightly touching the engine. After re-seating the wires in their clips, the last of the alternator whine is gone. Should have been obvious, but I’m new to this.

 

drill it right into the inner fender